A full model fit to shortest component 0.4y.
The residual of the fit across the entire spectrum (Nyquist T = 1/6 y) appears to be flat white noise
No use trying to improve the fit beyond this point --
>>>>>"Bottom line: when the residuals fail to be white noise, a different model should be tried. Short answer regarding time series regression: If they are not white noise (i.e. they are not normal, not have zero mean or serially autocorrelated), then your model is not fully adequate. Therefore, you should revise your model."